Silane recirculation for rapid carbon/silicon carbide or silicon carbide/silicon carbide ceramic matrix composites

ABSTRACT

A system for chemical vapor densification includes a reaction chamber having an inlet and outlet; a trap; a conduit fluidly coupled between the outlet of the reaction chamber and the trap; a cryogenic cooler fluidly coupled to the trap though a frustoconical conduit; a first exit path from the cryogenic cooler that vents hydrogen gas to an exhaust; and a second exit path from the cryogenic cooler that recirculates silane and hydrocarbon-rich gas back to the inlet of the reaction chamber—and a related method places a substrate in the reaction chamber; establishes a sub-atmospheric pressure inert gas atmosphere within the reaction chamber; densifies the substrate by inputting virgin gas into the reaction chamber; withdraws effluent gas from the reaction chamber; extracts silane and hydrocarbon-rich gas from the effluent gas; and recirculates the silane and hydrocarbon-rich gas back to the reaction chamber.

FIELD

The present disclosure relates to chemical vapor infiltration (CVI)and/or carbon vapor deposition (CVD) processes used to densifycomponents, including systems and methods of chemical vapordensification using recirculated and/or recycled hydrocarbon, silane,and/or carbosilane gases.

BACKGROUND

Carbon fiber and carbon matrix (C/C) composites are used in theaerospace industry to manufacture aircraft brake heat sink materials,among other applications. Similarly, silicon carbide (SiC) based ceramicmatrix composites (CMCs) are also used as suitable aircraft brakematerials, as well as within other industries, too (e.g., automotive,locomotive, engines, etc.). In various embodiments, CMC composites areproduced using, for example, chemical vapor infiltration (CVI) and/orchemical vapor deposition (CVD) processes. Referring generally, CVI andCVD processes place substrates (e.g., porous preforms) into reactorfurnaces and introduce gaseous precursors to form SiC depositions withinthe pores of the substrates. The SiC may be deposited in a series of oneor more infiltrations coatings, including whereby the substrates aredensified with carbon or other constitutents and then with SiC, or withSiC and then carbon or other constitutents. This collective process isgenerally referred to as chemical vapor densification.

In various CVI and CVD densification processes, by-product depositsaccumulate within various components of CMC manufacturing systems, suchas within their exhaust piping and/or plumbing systems. Since theby-product deposits can be reactive, and even pyrophoric, variousprecautions are undertaken to promote safe manufacturing environments.For example, conventional CMC manufacturing systems are shut down forlengthy periods of time while operators manually clean the componentsand piping to remove the by-product deposits. However, since thesecleaning procedures involve shutting down the CMC manufacturing systemsfor periods of time, they decrease the systems' capacities andthroughputs. In addition, build-up of condensable hydrocarbon tars fromconventional carbon CVI and CVD processes, although not pyrophoric innature, can also cause unintended reactions within various CMCmanufacturing systems.

SiC deposition commonly uses methyltrichlorosilane (MTS) as a sourcechemical. By-products from decomposing MTS, however, include theafore-mentioned pyrophoric condensates, as well as hydrochloric acid.These caustic effluents require suitable mitigation, and eliminatingand/or reducing them increases CMC manufacturing systems' and/ormethods' throughput, among other benefits. In addition, unusedhydrocarbon reaction exhaust and other gases (effluent) can be burnedoff and/or used to power an externality. Also, reducing processing timeand waste can reduce the costs of production and the emission ofgreenhouse gases.

SUMMARY

In various embodiments: a system for chemical vapor densificationincludes at least the following: a reaction chamber having an inlet andoutlet; a trap; a conduit fluidly coupled between the outlet of thereaction chamber and the trap; a cryogenic cooler fluidly coupled to thetrap though a frustoconical conduit; a first exit path from thecryogenic cooler that vents hydrogen gas to an exhaust; and a secondexit path from the cryogenic cooler that recirculates silane andhydrocarbon-rich gas back to the inlet of the reaction chamber.

In various embodiments, the trap and the cryogenic cooler are configuredto extract the silane and hydrocarbon-rich gas; and/or the trap isconfigured to filter at least one of hydrocarbon including four or morecarbon atoms, silane including three or more silicon atoms, andcarbosilane including a combination of four or more carbon or siliconatoms; and/or the cryogenic cooler is configured to condense at leastone of hydrocarbon including four or more carbon atoms, silane includingthree or more silicon atoms, and carbosilane including a combination offour or more carbon or silicon atoms; and/or the cryogenic cooler iscooled by helium; and/or the cryogenic cooler is cooled by liquidnitrogen; and/or an electric arc is intermediate the outlet and thetrap; and/or the electric arc creates a plasma material; and/or theplasma material is configured to fragment at least one of hydrocarbonincluding four or more carbon atoms, silane including three or moresilicon atoms, and carbosilane including a combination of four or morecarbon or silicon atoms; and/or a thermal oxidizer is at a terminal endof the first exit path.

In various embodiments: a method of chemical vapor densificationincludes at least the following: placing a substrate in a reactionchamber; establishing a sub-atmospheric pressure inert gas atmospherewithin the reaction chamber; densifying the substrate by inputtingvirgin gas into the reaction chamber; withdrawing effluent gas from thereaction chamber; extracting silane and hydrocarbon-rich gas from theeffluent gas; and recirculating the silane and hydrocarbon-rich gas backto the reaction chamber.

In various embodiments, the method further includes extracting hydrogengas from the effluent gas; and/or oxidizing the hydrogen gas to reactany silane contaminants that are not extracted from the effluent gas;and/or venting the hydrogen gas to an exhaust; and/or the extractingincludes applying an electric arc to the effluent gas, and wherein theelectric arc fragments at least one of hydrocarbon including four ormore carbon atoms, silane including three or more silicon atoms, andcarbosilane including a combination of four or more carbon or siliconatoms; and/or the extracting includes filtering at least one ofhydrocarbon including four or more carbon atoms, silane including threeor more silicon atoms, and carbosilane including a combination of fouror more carbon or silicon atoms; and/or the extracting includescondensing at least one of hydrocarbon including four or more carbonatoms, silane including three or more silicon atoms, and carbosilaneincluding a combination of four or more carbon or silicon atoms; and/orthe method further includes additionally densifying the substrate usingthe recirculated silane and hydrocarbon-rich gas.

In various embodiments: a method of chemical vapor densificationincludes at least the following: placing a substrate in a reactionchamber; establishing a sub-atmospheric pressure inert gas atmospherewithin the reaction chamber; densifying the substrate by inputtingvirgin gas into the reaction chamber; withdrawing effluent gas from thereaction chamber; extracting silane and hydrocarbon-rich gas from theeffluent gas; recirculating the silane and hydrocarbon-rich gas back tothe reaction chamber; extracting hydrogen from the effluent gas;oxidizing the hydrogen to react any silane contaminants that are notextracted from the effluent gas; venting the hydrogen to an exhaust; andadditionally densifying the substrate using the recirculated silane andhydrocarbon-rich gas; wherein the extracting silane and hydrocarbon-richgas from the effluent gas includes filtering and condensing at least oneof hydrocarbon including four or more carbon atoms, silane includingthree or more silicon atoms, and carbosilane including a combination offour or more carbon or silicon atoms.

In various embodiments, the extracting silane and hydrocarbon-rich gasfrom the effluent gas further includes applying an electric arc to theeffluent gas, and wherein the electric arc begins fragmenting thehydrocarbon, silane, or carbosilane molecules.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of a system for chemical vapordeposition comprising an exit path and a recirculation path used todensify components within a reaction chamber, in accordance with variousembodiments;

FIG. 2 illustrates a first method of chemical vapor deposition suitablefor densifying components, in accordance with various embodiments; and

FIG. 3 illustrates a second method of chemical vapor deposition suitablefor densifying components, in accordance with various embodiments.

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may beobtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsgenerally denote like elements.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration. While these exemplary embodiments are described insufficient detail to enable those skilled in the art to practice theexemplary embodiments of the disclosure, it should be understood thatother embodiments may be realized and that logical changes andadaptations in design and construction may be made in accordance withthis disclosure and the teachings herein. Thus, the detailed descriptionherein is presented for purposes of illustration only and notlimitation. The steps recited in any of the method or processdescriptions may be executed in any order and are not necessarilylimited to the order presented. Furthermore, any reference to singularincludes plural embodiments, and any reference to more than onecomponent or step may include a singular embodiment or step. Also, anyreference to attached, fixed, connected or the like may includepermanent, removable, temporary, partial, full and/or any other possibleattachment option. Additionally, any reference to without contact (orsimilar phrases) may also include reduced contact or minimal contact.

Referring now to FIG. 1, a system 10 for chemical vapor densification(e.g., chemical vapor infiltration (CVI) and/or chemical vapordeposition (CVD)) is illustrated, comprising both an exit path and arecirculation path, as elaborated upon further herein. In variousembodiments, the system 10 is particularly suited for densifying carbon,such as carbon fiber and/or carbon matrix (C/C) composites, as well assilicon carbide (SiC) based ceramic matrix composites (CMCs), etc.—suchas suitable for use, for example, in the aerospace industry, includingfor making aircraft brake heat sink materials, as well as for othervarious applications, too.

Referring now more specifically, the system 10 includes a reactionchamber 12 having a retort 14 that defines a reaction zone 16 within thereaction chamber 12. In various embodiments, the retort 14 comprises alid 18 that is configured to have a Venturi effect. For example, invarious embodiments, the lid 18 has a frustoconical shape and/orcomprises a Venturi cone. In various embodiments, the lid 18 is locatedproximate to, and/or includes, a sealable outlet 20 for the reactionchamber 12. In various embodiments, the reaction chamber 12 comprises avacuum-tight, sealable furnace/oven for chemical vapor densification(e.g., CVI and/or CVD processing).

In various embodiments, the reaction chamber 12 is generally cylindricaland scalable up and/or down as desired for various applications,including appropriately scaling other components of the system 10 aswell. In various embodiments, the system 10 is controlled by engineeringsoftware that collects data and/or controls the system 10, including inreal-time, in various embodiments. In various embodiments, a pressurewithin the system 10 is maintained at or below a predetermined setpressure of, approximately, 100 Torr (13,332.2 pascal (Pa)), includingeither at a constant set pressure and/or as pulsed from a low pressureto the predetermined set pressure. In various embodiments, otherpressures and/or arrangements are suited.

In various embodiments, a support 22 is located within the reaction zone16 of the reaction chamber 12 and supports one or more substrates 24located and/or placed within the reaction chamber 12 to begin theCVI/CVD process. In various embodiments, the support 22 is electricallyisolated from the rest of the reaction chamber 12, such as comprising anin-situ electrically isolated sample balance and/or load cell. Invarious embodiments, the substrates 24 include, for example, poroussubstrates, carbon fiber preforms, silicon carbide fiber preforms, closepacked particulates with silicon carbide, etc. In various embodiments,the substrates 24 are charged or grounded by an AC voltage that isfrequency-varied and positively or negatively biased. In variousembodiments, the substrates 24 are charged or grounded by a DC voltagethat is positively or negatively biased. In various embodiments, variouswalls of the retort 14 are grounded, negatively charged, or positivelycharged, as suited for particular applications. In various embodiments,the various walls of the retort 14 are isolated from the substrates 24.

In various embodiments, virgin gas is input into the reaction zone 16from a virgin gas source 26 via an inlet 28 into the reaction chamber12, the inlet 28 being generally distal the outlet 20 of the reactionchamber 12. As used herein, “virgin gas” is gas that has not yet flowedthrough the reaction chamber 12 and/or not yet been previouslyrecirculated/recycled within the system 10. Virgin gases may include,but are not limited to, disilane and/or silane, including in combinationwith one or more hydrocarbon reactive gases, such as butane, ethane,methane, natural gas mixtures, propane, and/or other hydrocarbonreactive gases.

In various embodiments, a mass flow controller 30 is intermediate thevirgin gas source 26 and the inlet 28 and controls and/or measures aflow rate of the virgin gas from the virgin gas source 26 into thereaction zone 16 of the reaction chamber 12. For example, in variousembodiments, the mass flow controller 30 allows and/or causes the virgingas source 26 to output between, approximately, 0-150 liters/minute(0-39.6 gallons/minute) of virgin gas into the reaction zone 16; and/orbetween, approximately, 0-100 liters/minute (0-26.4 gallons/minute);and/or between, approximately, 0-50 liters/minute (0-13.2gallons/minute). In various embodiments, the mass flow controller 30changes the amount of virgin gas input into the reaction zone 16 fromthe virgin gas source 26 in real-time, such as in response to theCVI/CVD processes (e.g., in conjunction with suitable sensors 82 and/orthe like) and/or based on other adjustments to the system 10 as well.

In various embodiments, one or more inert gas inlets 32 are also fluidlycoupled to the reaction chamber 12. In various embodiments, inert,and/or substantially inert (i.e., less reactive), gases (e.g., argon,helium nitrogen (N₂), xenon, etc.) are input from the one or more inertgas inlets 32 into the reaction chamber 12 in order to force atmosphericgases out of the reaction zone 16.

In various embodiments, effluent gas exits the reaction zone 16 via theoutlet 20 during and/or following densification. Upon exiting the outlet20, the effluent gas is directed through one or more conduits 34, 36enroute to a trap 38.

In various embodiments, an electric arc is used downstream of the outlet20 and intermediate the outlet 20 and the trap 38, such as a variablefrequency or fixed DC corona plasma 40 and an array of plasma conduits42 located between the outlet 20 and the trap 38 along the conduits 34,36. In various embodiments, the plasma 40 begins fragmenting heavyhydrocarbons, silanes, and/or carbosilanes from the effluent gas,including principally as liquids and/or tars, in order to begin breakingdown and starting to form lighter hydrocarbon and silane reaction gasesfor subsequent recirculating and/or recycling back to the reactionchamber 12. In this context, hydrocarbons, silanes, and/or carbosilanesare considered “heavy” when they comprise four or more (e.g., four orfive) carbon and/or silicon atoms and “light” when they comprise threeor fewer (e.g., zero to three) carbon and/or silicon atoms.

In various embodiments, the array of plasma conduits 42 beginfragmenting heavier hydrocarbons, silane, and/or carbosilane chainscomprising four or more (e.g., four or five) carbon and/or silicon atomsinto lighter hydrocarbons, silane, and/or carbosilane chains comprisingthree or fewer carbon and/or silicon atoms.

In various embodiments, the hydrocarbons, silane, and/or carbosilanechains exiting the outlet 20 along with the effluent gas cross the arrayof plasma conduits 42 in order to continue exiting from the conduit 36.

In various embodiments, a frequency and/or voltage applied by the arrayof plasma conduits 42 is selected to begin breaking down particularmolecule sizes. In various embodiments, for example, the frequencyand/or voltage of the array of plasma conduits 42 is selected tofragment hydrocarbon, silane, and/or carbosilane molecules comprisingfour or more (e.g., four or five) carbon and/or silicon atoms.

In various embodiments, the trap 38, which is downstream of the reactionchamber 12, comprises a whipper 44 having one or more sets of rotatingblades configured to filter (i.e., to remove) heavy hydrocarbons,silanes, and/or hydrocarbons from the effluent gas. For example, thetrap 38 causes heavier hydrocarbons, silane, and/or carbosilanemolecules, such as hydrocarbons, silane, and/or carbosilane moleculeshaving four or more (e.g., four or five) carbon and/or silicon atoms, tofilter out lighter hydrocarbons, silane, and/or carbosilane, such ashydrocarbons, silane, and/or carbosilane molecules having less than fourcarbon and/or silicon atoms. As a result, the trap 38 comprises a stageone trap, in various embodiments, configured to filter heavyhydrocarbons, silanes, and/or hydrocarbons.

In various embodiments, the trap 38 is also in fluid communication witha downstream cryogenic cooler 46, such as a helium cryogenic cooler,cooled by helium, and/or a liquid nitrogen condenser, cooled by liquidnitrogen. In various embodiments, the cryogenic cooler 46 is configuredto condense the light hydrocarbons, silanes, and/or hydrosilanes exitingfrom the trap 38. For example, the cryogenic cooler 46 causes the lighthydrocarbons, silane, and/or carbosilane molecules, such ashydrocarbons, silane, and/or carbosilane molecules having three or fewercarbon and/or silicon atoms, to condense, leaving still lighterhydrocarbons, silane, and/or carbosilane, such as hydrocarbons, silane,and/or carbosilane molecules having two or fewer carbon and/or siliconatoms. As a result, the cryogenic cooler 46 comprises a stage two trap,in various embodiments, configured to condense light hydrocarbons,silanes, and/or hydrocarbons

In various embodiments, the cryogenic cooler 46 also comprises ahydrogen extraction component. For example, in various embodiments, thecryogenic cooler 48 comprises a membrane filter to extract excesshydrogen as hydrogen gas (H₂), which evolves as the hydrocarbons,silane, and/or carbosilane condense within the cryogenic cooler 46.

Filtering and/or condensing hydrocarbons, silane, and/or carbosilanegases allows hydrogen, which remains in a gaseous state, to be extractedfrom the effluent gas output from the outlet 20 of the reaction chamber12.

Within the system 10, a first frustoconical conduit 48 couples the trap38 to the cryogenic cooler 46, in various embodiments. In variousembodiments, the first frustoconical conduit 48 facilitates a Venturieffect between the trap 38 and the cryogenic cooler 46, including viacompression.

In various embodiments, gaseous hydrogen exits the cryogenic cooler 46along an exit path 50 (representatively comprising arrows 50 a, 50 b, 50c, 50 d, 50 e, 50 f, and 50 g), as elaborated upon herein.

Within the system 10, a second frustoconical conduit 52 forms a separateexit from the cryogenic cooler 46 via an alternative exit conduit 54. Invarious embodiments, the second frustoconical conduit 52 facilitates aVenturi effect between the cryogenic cooler 46 and the alternative exitconduit 54, including via expansion.

In various embodiments, expanding hydrocarbons exiting the cryogeniccooler 46 via the second frustoconical conduit 52 facilitate a phasechange of the hydrocarbons, silane, and/or carbosilane from a liquidstate to a gaseous state. Once all, or most, of the hydrogen is removedfrom the effluent stream, the liquefied hydrocarbons, silanes, orcarbosilanes are heated within, or shortly after, the exit conduit 54 byan in-line heater 56, in various embodiments. This heating returns thesmall hydrocarbons, silanes, or carbosilanes to a gaseous state.

In various embodiments, a valve 58 in communication with the exitconduit 54 is opened, and one or more of a primary pump 60 and/orsecondary pump 62, located along a recirculation path 64 downstream ofthe second frustroconcial conduit 52, are activated in order to drawgaseous hydrocarbons, silane, and/or carbosilane from the exit conduit54 and into the recirculation path 64 (representatively comprisingarrows 64 a, 64 b, 64 c, 64 d, 64 e, 64 f, and 64 g).

In various embodiments, flow through the recirculation path 64 iscontrolled via the valve 58, the primary pump 60, and/or the secondarypump 62. In various embodiments, a one-way flow valve 66 and/or flowmeter 68 is/are intermediate the secondary pump 62 and the inlet 28 ofthe reaction chamber 12. In various embodiments, one or more of thevalve 58, the primary pump 60, and/or the secondary pump 62 control theflow of recirculated gas back into the reaction chamber 12.

In various embodiments, this recirculated gas and virgin gas from thevirgin gas source 26 are separately input back into the reaction chamber12 via the inlet 28 (e.g., via discrete entrances). In variousembodiments, the recirculated gas and the virgin gas from the virgin gassource 26 are mixed at the inlet 28 prior to being introduced into thereaction chamber 12.

In various embodiments, hydrocarbon gases, including heavy hydrocarbons,silanes, and carbosilanes are recycled/recirculated to improve the rateof densification and/or efficiency of the CVI/CVD processes within thesystem 10, which continue after the gases recirculate through therecirculation path 64.

Referring again to the exit path 50 from the cryogenic cooler 46, flowof the effluent gas and/or hydrogen gas extracted by the cryogeniccooler 46 is controlled via an exit valve 70, a throttle valve 72, aturbo pump 74, a roughing pump 76, and/or a thermal oxidizer 78 disposedin generally serial communication with one another downstream along theexit path 50. In various embodiments, discharge from the thermaloxidizer 78 is vented to an exhaust 80 of the system 10.

In various embodiments, pressure within the exit path 50 is maintainedat a desired level by opening and closing the exit valve 70 and/or thethrottle valve 72, as well as by decreasing and/or increasing the speedof the turbo pump 74 and/or the roughing pump 76.

In various embodiments, one or more pressure transducers/sensors 82 arealso located throughout the system 10, such as to measure flow levels atvarious points within the system 10.

As described herein, recirculated effluent gases within the system 10increase a number of moles of small carbon and/or silicon moleculesflowing through the reaction zone 16 of the reaction chamber 12 and thatare available for additional CVI/CVD processing of the substrate 24,including without increasing the flow and/or amount of virgin (i.e.,initial) gas input into the system 10 from the virgin gas source 26.This decreases the amount of, for example, methane, as a virgin gas,that is used in densification, which has positive green-house effects,in various embodiments. In addition, the recirculated silane is morereactive than methane, in various embodiments. In addition, the system10 also alleviates machining the substrate 24 to re-open surface poresthereon that can close during densification. As a result, therecirculated silane gases within the system 10 increase thedensification rate of the substrate 24, including as more effectivemolecules pass through the reaction zone 16 of the reaction chamber 12and increase a number of molecules that make collisions (i.e., have anopportunity to bond with) with the substrate 24. Accordingly, in variousembodiments, the system 10 (and methods below) allows enhanced and/orfaster densification of the substrate 24, including greater than, forexample, 2.0 g/cc, as well as greater throughput, reduced by-productmitigation, etc.

Referring now also to FIGS. 1-2, a method 200 for chemical vapordensification (e.g., chemical vapor infiltration (CVI) and/or chemicalvapor deposition (CVD)) is illustrated, in accordance with variousembodiments. More specifically, the method 200 begins at a step 202,after which one or more substrates are placed in a reaction chamber instep 204, such as placing the one or more substrates 24 of FIG. 1 intothe reaction chamber 12 of FIG. 1. Thereafter, inert gas is input intothe reaction chamber to establish a sub-atmospheric pressure within thereaction chamber in step 206, such as from one or more inert gas sources32 of FIG. 1. In various embodiments, the inert, and/or substantiallyinert, gases include one or more of argon, helium, nitrogen (N2), xenon,etc., and they force atmospheric gases out of the reaction chamber. Invarious embodiments, the sub-atmospheric pressure is maintained at orbelow a predetermined set pressure of, approximately, 100 Torr (13,332.2pascal (Pa)), including either at a constant set pressure and/or aspulsed from a low pressure to the predetermined set pressure. In variousembodiments, other pressures and/or arrangements are suited. After theinert gas is input into the reaction chamber in step 206, one or morevirgin gases, including various combinations thereof, are input into thereaction chamber to densify the substrate in step 208, such as from thevirgin gas source 26 of FIG. 1. In various embodiments, the virgin gasesmay include, but are not limited to, disilane and/or silane, includingin combination with one or more hydrocarbon reactive gases, such asbutane, ethane, methane, natural gas mixtures, propane, and/or otherhydrocarbon reactive gases. Thereafter, effluent gas is withdrawn fromthe reaction chamber in step 210. Thereafter, silane andhydrocarbon-rich gas are extracted from the effluent gas in step 212. Invarious embodiments, the silane and hydrocarbon-rich gas are extractedfrom the effluent gas using a trap and/or a cryogenic cooler, such asthe trap 38 and cryogenic cooler 46 of FIG. 1. In various embodiments,the trap includes a whipper having one or more sets of rotating bladesconfigured to filter (i.e., to remove) heavy (e.g., comprising four tosix carbon and/or silicon atoms) hydrocarbons, silanes, and/orhydrocarbons from the effluent gas, such as the whipper 44 of FIG. 1. Invarious embodiments, the cryogenic cooler condenses light (e.g.,comprising three or fewer carbon and/or silicon atoms) hydrocarbons,silanes, and/or hydrocarbons from the effluent gas. In variousembodiments, the cryogenic cooler is cooled by helium and/or liquidnitrogen. In any event, after the silane and hydrocarbon-rich gas areextracted from the effluent gas in step 212, they are recirculatedand/or recycled back to the reaction chamber in step 214, after whichthe method 200 ends in a step 216.

In various embodiments, the method 200 further comprises one or more ofextracting hydrogen from the effluent gas, oxidizing the hydrogen,and/or venting the hydrogen to an exhaust, such as through the thermaloxidizer 78 of FIG. 1. In various embodiments, the method 200 furthercomprises applying an electric arc, such as a plasma 40 of FIG. 1, tothe effluent gas, wherein the electric arc begins fragmenting heavyhydrocarbon, silane, or carbosilane molecules comprised of four or more(e.g., four or five) carbon or silicon atoms, as part of, and/or as aprecursor to, the extraction process. In various embodiments, theextraction of the method 200 comprises filtering hydrocarbon, silane, orcarbosilane molecules comprised of four or more (e.g., four or five)carbon or silicon atoms. In various embodiments, the extraction of themethod 200 comprises condensing hydrocarbon, silane, or carbosilanemolecules comprised of four or more (e.g., four or five) carbon orsilicon atoms. In various embodiments, the method 200 further comprisesadditionally densifying the substrate using the recirculated silane andhydrocarbon-rich gas.

Referring now also to FIGS. 1 and 3, a method 300 for chemical vapordensification (e.g., chemical vapor infiltration (CVI) and/or chemicalvapor deposition (CVD)) is illustrated, in accordance with variousembodiments. More specifically, the method 300 begins at a step 302,after which one or more substrates are placed in a reaction chamber instep 304, such as placing the one or more substrates 24 of FIG. 1 intothe reaction chamber 12 of FIG. 1. Thereafter, inert gas is input intothe reaction chamber 12 to establish a sub-atmospheric pressure withinthe reaction chamber 12 in step 306, such as from one or more inert gassources 32 of FIG. 1. In various embodiments, the inert, and/orsubstantially inert, gases include one or more of argon, helium,nitrogen (N2), xenon, etc., and they force atmospheric gases out of thereaction chamber 12. In various embodiments, the sub-atmosphericpressure is maintained at or below a predetermined set pressure of,approximately, 100 Torr (13,332.2 pascal (Pa)), including either at aconstant set pressure and/or as pulsed from a low pressure to thepredetermined set pressure. In various embodiments, other pressuresand/or arrangements are suited. After the inert gas is input into thereaction chamber 12 in step 306, one or more virgin gases, includingvarious combinations thereof, are input into the reaction chamber 12 todensify the substrate in step 308, such as from the virgin gas source 26of FIG. 1. In various embodiments, the virgin gases may include, but arenot limited to, disilane and/or silane, including in combination withone or more hydrocarbon reactive gases, such as butane, ethane, methane,natural gas mixtures, propane, and/or other hydrocarbon reactive gases.Thereafter, effluent gas is withdrawn from the reaction chamber 12 instep 310. Thereafter, silane and hydrocarbon-rich gas are extracted fromthe effluent gas in step 312. In various embodiments, the silane andhydrocarbon-rich gas are extracted from the effluent gas using a trapand/or a cryogenic cooler, such as the trap 38 and cryogenic cooler 46of FIG. 1. In various embodiments, the trap 38 includes a whipper havingone or more sets of rotating blades configured to filter (i.e., toremove) heavy (e.g., comprising four to six carbon and/or silicon atoms)hydrocarbons, silanes, and/or hydrocarbons from the effluent gas, suchas the whipper 44 of FIG. 1. In various embodiments, the cryogeniccooler 46 condenses light (e.g., comprising three or fewer carbon and/orsilicon atoms) hydrocarbons, silanes, and/or hydrocarbons from theeffluent gas. In various embodiments, the cryogenic cooler 46 is cooledby helium and/or liquid nitrogen. In any event, after the silane andhydrocarbon-rich gas are extracted from the effluent gas in step 312,they are recirculated and/or recycled back to the reaction chamber 12 instep 314. In addition to extracting the silane and hydrocarbon-rich gasfrom the effluent gas in step 312, hydrogen is also extracted from theeffluent gas in step 316, oxidized in step 318, such as by using thethermal oxidizer 78 of FIG. 1, and vented in step 320. In variousembodiments, the hydrogen waste stream is oxidized in order to safelyreact any silane contaminants that made it past the trap 38 and/orcryogenic cooler 46. In addition, the one or more substrates areadditionally densified using the recirculated silane andhydrocarbon-rich gas in step 322, after which the method 300 ends in astep 324.

As described herein, systems and methods extract silane andhydrocarbon-rich gas from an effluent gas downstream of a chemical vapordensification furnace, such as a CVI/CVD reaction chamber, used todensify substrates, such as used in the aerospace industry. In variousembodiments, the silane and hydrocarbon-rich gas are subjected to beingfiltered by a trap having a whipper and/or condensed by a cryogeniccooler. In various embodiments, the trap comprises a stage one trap, andthe cryogenic cooler comprises a stage two trap. In various embodiments,heavier and/or longer hydrocarbons, silane, and/or carbosilanemolecules, such as hydrocarbons, silane, and/or carbosilane moleculeshaving four or more (e.g., four or five) carbon and/or silicon atoms,are treated, leaving lighter and/or shorter hydrocarbons, silane, and/orcarbosilane, such as hydrocarbons, silane, and/or carbosilane moleculeshaving four or fewer carbon and/or silicon atoms. In variousembodiments, the silane and hydrocarbon-rich gas is recirculated back tothe furnace and combined with new virgin gases to additionally densifythe substrate, decreasing the amount of time required to do so (i.e.,the number of hours on gas), as well as increasing the effectiveness ofthe densification. In various embodiments, an electric arc, such as aplasma, is used to fragment the chemical species in the effluent gasstream—i.e., to begin breaking down the hydrocarbons, silanes, and/orcarbosilanes from the effluent gas, including principally as liquidsand/or tars, in order to further treat the hydrocarbon and silanereaction gases for subsequent recirculating and/or recycling back to thefurnace. In various embodiments, hydrogen is also extracted from theeffluent gas stream and vented, such as through a thermal oxidizer.

Various technical effects of the foregoing include increasing theefficacy of chemical vapor densification and/or decreasing the number ofcycles, power, and/or time required to achieve a desired efficacy, aswell as mitigating the effects of by-products created during theprocess. The recirculated and/or recycled silane and hydrocarbon-richgas improve overall chemical vapor densification (e.g., CVI and/or CVD)processes.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures included herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure.

The scope of the disclosure is accordingly to be limited by nothingother than the appended claims, in which reference to an element in thesingular is not intended to mean “one and only one” unless explicitly sostated, but rather “one or more.” It is to be understood that unlessspecifically stated otherwise, references to “a,” “an,” and/or “the” mayinclude one or more than one and that reference to an item in thesingular may also include the item in the plural. All ranges and ratiolimits disclosed herein may be combined.

Moreover, where a phrase similar to “at least one of A, B, and C” isused in the claims, it is intended that the phrase be interpreted tomean that A alone may be present in an embodiment, B alone may bepresent in an embodiment, C alone may be present in an embodiment, orthat any combination of the elements A, B and C may be present in asingle embodiment; for example, A and B, A and C, B and C, or A and Band C. Different cross-hatching is used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

The steps recited in any of the method or process descriptions may beexecuted in any order and are not necessarily limited to the orderpresented. Furthermore, any reference to singular includes pluralembodiments, and any reference to more than one component or step mayinclude a singular embodiment or step. Elements and steps in the figuresare illustrated for simplicity and clarity and have not necessarily beenrendered according to any particular sequence. For example, steps thatmay be performed concurrently or in different order are illustrated inthe figures to help to improve understanding of embodiments of thepresent disclosure.

Surface shading lines, if any, may be used throughout the figures todenote different parts or areas but not necessarily to denote the sameor different materials. In some cases, reference coordinates may bespecific to each figure.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment,” “an embodiment,”“various embodiments,” etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element is intended to invoke 35 U.S.C. 112(f)unless the element is expressly recited using the phrase “means for.” Asused herein, the terms “comprises,” “comprising,” or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus.

What is claimed is:
 1. A system for chemical vapor densification,comprising: a reaction chamber having an inlet and outlet; a trap; aconduit fluidly coupled between the outlet of the reaction chamber andthe trap; a cryogenic cooler fluidly coupled to the trap though afrustoconical conduit; a first exit path from the cryogenic cooler thatis configured to vent hydrogen gas to an exhaust; and a second exit pathfrom the cryogenic cooler that is configured to recirculate silane andhydrocarbon-rich gas back to the inlet of the reaction chamber.
 2. Thesystem for chemical vapor densification of claim 1, wherein the trap andthe cryogenic cooler are configured to extract the silane andhydrocarbon-rich gas.
 3. The system for chemical vapor densification ofclaim 1, wherein the trap is configured to filter at least one ofhydrocarbon comprised of four or more carbon atoms, silane comprised ofthree or more silicon atoms, and carbosilane comprised of a combinationof four or more carbon or silicon atoms.
 4. The system for chemicalvapor densification of claim 1, wherein the cryogenic cooler isconfigured to condense at least one of hydrocarbon comprised of four ormore carbon atoms, silane comprised of three or more silicon atoms, andcarbosilane comprised of a combination of four or more carbon or siliconatoms.
 5. The system for chemical vapor densification of claim 1,wherein the cryogenic cooler is configured to be cooled by helium. 6.The system for chemical vapor densification of claim 1, wherein thecryogenic cooler is configured to be cooled by liquid nitrogen.
 7. Thesystem for chemical vapor densification of claim 1, further comprising:an electric arc intermediate the outlet and the trap.
 8. The system forchemical vapor densification of claim 7, wherein the electric arc isconfigured to create a plasma material.
 9. The system for chemical vapordensification of claim 8, wherein the plasma material is configured tofragment at least one of hydrocarbon comprised of four or more carbonatoms, silane comprised of three or more silicon atoms, and carbosilanecomprised of a combination of four or more carbon or silicon atoms. 10.The system for chemical vapor densification of claim 1, furthercomprising: a thermal oxidizer at a terminal end of the first exit path.11. A method of chemical vapor densification, comprising: placing asubstrate in a reaction chamber; establishing a sub-atmospheric pressureinert gas atmosphere within the reaction chamber; densifying thesubstrate by inputting virgin gas into the reaction chamber; withdrawingeffluent gas from the reaction chamber; extracting silane andhydrocarbon-rich gas from the effluent gas; and recirculating the silaneand hydrocarbon-rich gas back to the reaction chamber.
 12. The method ofchemical vapor densification of claim 11, further comprising: extractinghydrogen gas from the effluent gas.
 13. The method of chemical vapordensification of claim 12, further comprising: oxidizing the hydrogengas to react any silane contaminants that are not extracted from theeffluent gas.
 14. The method of chemical vapor densification of claim13, further comprising: venting the hydrogen gas to an exhaust.
 15. Themethod of chemical vapor densification of claim 11, wherein theextracting comprises applying an electric arc to the effluent gas, andwherein the electric arc fragments at least one of hydrocarbon comprisedof four or more carbon atoms, silane comprised of three or more siliconatoms, and carbosilane comprised of a combination of four or more carbonor silicon atoms.
 16. The method of chemical vapor densification ofclaim 11, wherein the extracting comprises filtering at least one ofhydrocarbon comprised of four or more carbon atoms, silane comprised ofthree or more silicon atoms, and carbosilane comprised of a combinationof four or more carbon or silicon atoms.
 17. The method of chemicalvapor densification of claim 11, wherein the extracting comprisescondensing at least one of hydrocarbon comprised of four or more carbonatoms, silane comprised of three or more silicon atoms, and carbosilanecomprised of a combination of four or more carbon or silicon atoms. 18.The method of chemical vapor densification of claim 11, furthercomprising: additionally densifying the substrate using the recirculatedsilane and hydrocarbon-rich gas.
 19. A method of chemical vapordensification, comprising: placing a substrate in a reaction chamber;establishing a sub-atmospheric pressure inert gas atmosphere within thereaction chamber; densifying the substrate by inputting virgin gas intothe reaction chamber; withdrawing effluent gas from the reactionchamber; extracting silane and hydrocarbon-rich gas from the effluentgas; recirculating the silane and hydrocarbon-rich gas back to thereaction chamber; extracting hydrogen from the effluent gas; oxidizingthe hydrogen to react any silane contaminants that are not extractedfrom the effluent gas; venting the hydrogen to an exhaust; andadditionally densifying the substrate using the recirculated silane andhydrocarbon-rich gas; wherein the extracting silane and hydrocarbon-richgas from the effluent gas comprises filtering and condensing at leastone of hydrocarbon comprised of four or more carbon atoms, silanecomprised of three or more silicon atoms, and carbosilane comprised of acombination of four or more carbon or silicon atoms.
 20. The method ofchemical vapor densification of claim 19, wherein the extracting silaneand hydrocarbon-rich gas from the effluent gas further comprisesapplying an electric arc to the effluent gas, and wherein the electricarc begins fragmenting the hydrocarbon, silane, or carbosilanemolecules.